(a) Field of the Invention
The present invention relates to shutters for cameras, and more particularly, to a shutter for cameras arranged so that the shutter speed may be controlled by a gear governor.
(b) Description of the Prior Art
Generally, the gear governor to be used to control the shutter speed, that is, the exposure time consists of a gear train including an escape wheel and an anchor removably meshing with the escape wheel.
The conventional focal plane shutter is so arranged that the operations of meshing and separating the escape wheel and anchor may be made by a control cam for controlling the opening and closing of the shutter. As a result, in the operation of the shutter, the time interval until the operation as a governor is begun after the anchor is meshed with the escape wheel will be so short that the operation as a governor will be forced before the anchor is completely meshed with the escape wheel. Further, the mass of the above mentioned control cam is so comparatively small that the force for driving the governor will be likely to fluctuate. For the above mentioned reasons, in the conventional focal plane shutter, there has been a defect that particularly, in the low shutter speed range, that is, in the case that the exposure time of the shutter is comparatively long, the exposure time to be controlled will be inaccurate.
Further, in the gear governor to be used for the above mentioned object, particularly, in the terminal range of the gear train, not only each gear will rotate at a high speed but also its rotation will be started and stopped momentarily and, at the time of stopping it, a quick reversing action will occur due to the reaction by the inertia. This will be repeated whenever the shutter is operated. Therefore, the gears and pinions forming the gear train will be destroyed and the bearing parts will be broken so often as to be a main cause of the failure of the governor. In fact, most of the failures of the shutter are occupied by the failures of this kind of governors.